The snowpack structure is complex and varies throughout the region. A conservative approach is essential.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain on Monday
Weather Forecast
The Interior will see generally dry, cool conditions under the current NW flow. A Pacific frontal system will arrive overnight, bringing light- moderate amounts of precipitation and warmer temperatures.Sunday: Cloudy with snow amounts 10-15 cm. Alpine temperatures near -6. Light SW winds. Freezing levels near 1000 m. Monday: Snow amounts 15-25 cm. Alpine temperatures near -5. Moderate westerly ridgetop winds. Freezing levels 1300 m.Tuesday: Cloudy with sunny periods. Alpine temperatures near -7. Ridgetop winds light from the West. Freezing levels near 800 m.
Avalanche Summary
Several natural and rider triggered slab avalanches and loose-snow avalanches up to size 2 were reported on Friday.
Snowpack Summary
Average snowpack depths at treeline range from 100 cm -150 cm. New snow up to 15 cm has buried older wind slabs in exposed terrain at treeline and above. The new storm slab is touchy to rider triggers, and natural loose dry sluffing from steeper terrain exists. Buried down 40-60 cm is a surface hoar, and facet layer. This layer has recently been reactive to riders and natural triggers and both cracking and whumpfing have been noted.Digging deeper down 70-90 cm, is the late-November interface, which consists of a sun crust/ facet combo on steep south facing slopes and larger, proud surface hoar crystals in sheltered areas. This layer is generally considered to be "stubborn" to trigger. However, professionals are keeping a close eye on this layer especially with forecast new load.At the base of the snowpack the October crust is most predominant on north-facing alpine slopes with smooth ground cover. Triggering this weakness is unlikely, but if triggered the resulting avalanche would be very large and consequential.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.